The recent state of the art relating to valved keg closures is exemplified by U.S. Pat. No. 4,181,143 to M. R. Fallon and U.S. Pat. Nos. 4,142,658 and 4,150,771, both issued to C. G. Golding.
A keg intended to be equipped with a closure unit of the general type to which this invention relates has an opening in its top wall in which a bushing is permanently installed. An upper portion of the closure unit, in the form of a cylindrical element, is removably seated in the bushing and defines an upwardly opening well with a coaxial annular valve seat at its bottom. The well accommodates the bottom portion of a tapping coupler that can be readily detachably connected to the closure unit, and for such connection there are bayonet lugs on the top of the cylindrical element that project radially into the well.
The closure unit also comprises an elongated siphon tube which has a bottom end near the bottom of the keg and which is axially movable to carry a valve element at its top into and out of engagement with the valve seat in the cylindrical element. The siphon tube is biased upward, to urge the valve element towards its closed position, by means of a coiled compression spring that surrounds it near its upper end but in downwardly spaced relation to the valve element. The spring is in turn surrounded by a relatively stationary tubular element, substantially shorter than the siphon tube but of substantially larger diameter, which is coaxially fixed to the cylindrical element and projects down from it. Near its lower end this tubular element supports an annular spring seat against which the lower end of the spring is engaged and through which the siphon tube extends for guidance in its axial motion.
The bushing that is fixed in the keg has a radially inwardly projecting annular flange at its bottom, which underlies the cylindrical element of the closure unit and through which the stationary tubular element projects downward. Between this flange and the underside of the cylindrical element, closely surrounding the tubular element, there is a resilient sealing ring, and the cylindrical element is normally secured in the bushing in such a manner as to be under downward force whereby the sealing ring is axially compressed to provide a seal between the bushing and the closure unit.
Practically all commercial beer kegs are equipped with valved closures of this general character, in one form or another. Although such commercial success attests to a well developed state of the art, there is a pressing need and desire to achieve further improvements, because the industry concerned with the manufacture of keg closures is a vigorously competitive one that relies upon skill and ingenuity for the attainment of commercial advantage. The principal purchasers of keg closure units are breweries, which buy them in large quantities and on the basis of careful comparison of both cost and technical features. Thus, even a small difference in unit cost as between competitive closure units may have substantial commercial significance. Considering that the above identified patents were assigned to active manufacturers of closure units, and that they disclose devices now being successfully marketed, it will be apparent that those patents represent the farthest advance to date that has been attainable by skill in the art coupled with inventive ingenuity.
Although it is imperative that a satisfactory keg closure be inexpensive, low cost cannot be attained at the sacrifice of other essentials, including great sturdiness for resistance to extremely rough handling, complete reliability in the face of abusive treatment, and an inherent capability for being thoroughly and easily cleaned.
An overriding requirement is that the closure be safely removably from a keg in which it is installed. A valved closure normally remains in a keg through numerous trips to and from the brewery, as well as during the wash that precedes every fill, but it must be readily removable from the keg for repair or replacement. Because its removal could occur at a time when the keg is pressurized--and possibly even highly pressurized--the closure assembly must be secured in the keg in such a manner as to provide for a gas-tight seal between it and the keg and also provide for a removal procedure wherein the seal is opened to permit escape of substantially all pressure gas while the closure assembly continues to be restrained against separation from the keg, so that the assembly is released only after there is no danger of its being blown out.
The above identified Golding patents disclose assemblies wherein the upper cylindrical element of the closure unit has a direct threaded connection with the bushing that is fixed in the keg, so that the resilient sealing ring confined between the bushing and the cylindrical element is axially compressed by screwing the closure unit into the bushing. Such an arrangement is safe because the seal is opened for escape of gas from the keg before the cylindrical element is completely screwed out of the bushing. However, it is possible for the closure unit to be screwed so deeply into the keg bushing as to over-compress the resilient sealing ring, subjecting it to "compression set" that causes it to lose its sealing capability. Another important disadvantage of a direct threaded connection between the closure unit and the keg bushing is that torque imposed upon the closure unit when a tapping coupler is being disconnected from it can loosen the closure unit in the bushing, especially if the resilient sealing ring has become embrittled or taken a set, and thereupon the closure unit can come out of the keg with the tapping coupler.
The above identified Fallon patent discloses an arrangement that was intended to avoid overcompression of the sealing ring without sacrifice of safety and whereby the closure unit was confined against rotation under torque imposed upon it through the coupler. The cylindrical upper element of the closure unit had radially outwardly projecting lugs that were receivable in short axially extending upper keyway slots in the keg bushing, opening upwardly to its top edge and downwardly into a circumferential groove. When the cylindrical element had been inserted partway down into the bushing, its lugs engaged the bottom surface of the circumferential groove, and it then had to be rotated a fractional turn to bring its lugs into register with lower keyway slots that opened upwardly into said groove and extended a limited distance down from it. With its lugs bottomed in the lower keyway slots, the cylindrical element was in an axial position in which it subjected the resilient sealing ring to a desired amount of compression. The cylindrical element could be confined in that position by a radially expansible retainer ring overlying its top edge and received in the circumferential groove. Upon removal of the retainer ring, the cylindrical element could rise far enough for its lugs to engage the top surface of the circumferential groove, permitting escape of gas, but it could not be removed from the bushing until it had been rotated to align its lugs with the upper keyway slots. One evident disadvantage of this arrangement was that the groove and keyway slots in the bushing were somewhat difficult and expensive to machine. Furthermore, special equipment was needed for forcing the closure unit down against the resilience of the sealing ring so that the expansible retainer ring could be inserted into the circumferential groove.
In the earlier closure assemblies, the siphon tube had little guidance that confined it to purely axial motion, and consequently the valve on the top of that tube could be cocked or skewed out of coaxial relation to its seat if it was forced open by a probe or the like that acted at an inclination to its axis. Such skewing of the valve element could occur if the keg was tilted when in place on a washing or filling rack, as sometimes happened when the keg had been deformed by rough handling. In such cases, owing to the lack of guidance for the siphon tube, the valve element could maintain its skewed attitude as it re-engaged its seat on the cylindrical upper element of the closure, with the result that the closure leaked.
The Golding patents disclose a washer-like or spider-like guide element surrounding the upper portion of the siphon tube member, just below the valve element thereon, to provide a seat for the upper end of the compression spring that biases that tube member upwardly. Radially outer edge portions of this guide element slidingly engage the fixed tubular element surrounding the siphon tube member, cooperating with that tubular element to confine the siphon tube member to axial motion and restrain it against cocking and skewing. Although this spider-like part serves in the dual role of spring seat and guide element, the present invention reveals that both of these functions can be very satisfactorily performed without the need for a separate part, thus eliminating the cost of manufacturing and installing it.
The Golding patents focus upon means for providing a connection and seal between the upper cylindrical element of the closure assembly and the upper end of the tubular element that projects down into the keg from that cylindrical element. That connection must be a sturdy one because forces imposed upon the tubular element by the valve springs are transferred to the cylindrical element through it. Again, it has become apparent from the present invention that the expedients devised by Golding left something to be desired with respect to low cost and manufacturing simplicity.